ST4 916 Clutch: advice please?

[Martin C]

I’ve just been replacing the clutch on my ST4 (916 engine), using a Ducati clutch pack and outer basket. On assembly, the compressed plates were too far out, with the outermost friction plate able to disengage when the clutch was operated. Removing one of the two innermost plain plates appears to have solved this, tested with engine running, but expert advice is this shouldn’t be necessary.

The supplying dealer says the clutch centre (not replaced) “must have worn and moved outwards” - which I don’t understand, but also says removing the plate is correct. Does anyone have any ideas, please?

[slob]

you should have:
8 metal plates @2mm
1 dished metal plate @1.5mm
7 fibre plates @3mm
(8*2)+1.5+(3x7)=38.5 mm total stack height (new)

anything less than 36mm or more than 40mm is almost definitely going to cause a problem

the worn centre statement sounds odd to me too, without a good look it's hard to speculate

[Darren69]

yea,, if the clutch centre is tightened down then you just need to adjust/remove the plates to get the right stack height. I've not heard of that issue with the hub coming loose before so if it is down to spec just remove a plate and see if that sorts it.

[Dukedesmo]

The hub wearing is a thing, I had it on my 916. Basically the star shaped washer 'ate' into the body of the hub meaning the hub was effectively loose and, due to the springs pulling on it, ran about 2mm further out.

The retaining caps on the springs were actually rubbing on the clutch cover but I'm not sure if it's a common thing?

As for the clutch plates, the quantity is not important but the pack thickness is, I find anything over 38mm overall makes finding neutral at a stop difficult and if it's too thin (36mm maybe?) then you'll get slippage.

With regards to the first plain plates at the base, I don't see why using just 1 would be any worse than 2? In fact I have this in mine, along with using some 1.5mm plain plates in the stack to get the correct height but also, by reducing the overall thickness of plain plates you maybe able to get an extra friction plate in there which makes for a better, longer lasting clutch.

And, controversially to some purists, I don't use any dished plates at all as I see no benefit to having a plate that only gives partial surface contact with the adjacent frictions? and I've never had any problem in doing so.

[Mr Gazza]

Originally Posted by Dukedesmo

I don't use any dished plates at all as I see no benefit to having a plate that only gives partial surface contact with the adjacent frictions? and I've never had any problem in doing so.

I don't think the dished plate is actually dished when it is compressed by the springs.

I had my brand new EVR pack, complete with requested dished plate, between fingers and thumbs, I could easily squash the dished plate flat with finger pressure alone. I imagine the combined force of the clutch springs is far greater than I can exert with my hands.

I had the pack out this afternoon as it happens, I gave it it's annual little wipe over and check. All the plain plates had a "print" of the friction pads on each side including the dished plate, which could only have happened if the plate was squashed flat. There was no evidence of the dished plate having worn the friction pads with it's raised edge.
So I don't think it does have partial contact with the adjacent plates at all, rather that it has full contact until spring pressure is released by operating the clutch.

For the pedantic and observant; the plain pates that run as a pair together were not "printed" by the friction plates on their meeting faces as they don't contact them, nor do they rotate relative to one another. Same for the outer face meeting the pressure plate.

Further, as I can be a pedant, why do we insist on calling them friction plates when they operate by the principle of stiction? Friction is undesirable in a clutch!

[Dukedesmo]

Originally Posted by Mr Gazza

I don't think the dished plate is actually dished when it is compressed by the springs.

Maybe? but I still see no advantage to it and definitely no issue when not fitted, so I don't bother.

[Darren69]

Stiction is really just another fancy word for friction but in a more dynamic sense. and according to wikipedia "stiction might also be an illusion made by the rotation of kinetic friction" Whatever that means? lol

[slob]

I think the dished plate is meant to ease judder at the release point, I've heard advice to try a second (reversed) dished plate (at the other end of the pack) to smooth out a problem slipper clutch

[Martin C]

Originally Posted by Dukedesmo

The hub wearing is a thing, I had it on my 916. Basically the star shaped washer 'ate' into the body of the hub meaning the hub was effectively loose and, due to the springs pulling on it, ran about 2mm further out.

The retaining caps on the springs were actually rubbing on the clutch cover but I'm not sure if it's a common thing?.

Ah yes, my clutch’s star-shaped thrust washer has indeed somehow “sunk” into the hub, so that at first I thought it was missing. Presumably this is the effect of a steel washer being tightened at 186 Nm (aka “EFT”) onto an alloy centre. Now I understand what was meant by it having “worn and moved outwards”, many thanks for the explanation! Time for a new centre and thrust washer...

[Dukedesmo]

Originally Posted by Martin C

Ah yes, my clutch’s star-shaped thrust washer has indeed somehow “sunk” into the hub, so that at first I thought it was missing. Presumably this is the effect of a steel washer being tightened at 186 Nm (aka “EFT”) onto an alloy centre. Now I understand what was meant by it having “worn and moved outwards”, many thanks for the explanation! Time for a new centre and thrust washer...

Exactly what mine did.

On further examination I reckon I could have fitted another star washer on top and that might work by using the 'sunken' one as a spacer? but, knowing it's worn I'd rather replace it.

[Darren69]

Usually, everytime someone posts about clutch issues I generally respond with 'the standard Ducati clutch is rubbish' which quite honestly it is and that is usually the issue. Put a DP or good quality aftermarket one in there and your good to go.

[Luddite]

Originally Posted by Dukedesmo

Exactly what mine did.

On further examination I reckon I could have fitted another star washer on top and that might work by using the 'sunken' one as a spacer? but, knowing it's worn I'd rather replace it.

I thought that suggestion sounded familiar DD! Then I remembered that's what Andy of Andy's Motorcycle Obsessions did with his worn clutch. So it would appear to be an effective remedy if you're unable to replace the hub. It's mentioned at 8:50 in this video.

[Martin C]

Originally Posted by Martin C

Ah yes, my clutch’s star-shaped thrust washer has indeed somehow “sunk” into the hub, so that at first I thought it was missing. Presumably this is the effect of a steel washer being tightened at 186 Nm (aka “EFT”) onto an alloy centre. Now I understand what was meant by it having “worn and moved outwards”, many thanks for the explanation! Time for a new centre and thrust washer...

I'm glad to say that a new clutch centre and thrust washer resulted in the correct clearance to enable me to fit the complete set of new clutch plates. The thrust washer now sits about 2mm above the centre, which restored that amount of clearance for the final clutch plate.

I was warned that the new centre can be difficult to fit onto the cush-drive hub due to the 12 rubber pads, so between each pair of pads I first inserted a short rubber strip to hold the pads apart, then easily pushed the new centre on just by hand, then pulled the 6 spacers out via the centre hole. It was no problem, and also there is no detectable slack in the cush-drive.

Clutch action is greatly improved on the road, and the complete new clutch is slightly less rattly on tick-over.....

[jerry]

My S4 has never had that spider plate since it was new ,, works fine although i have fitted ally basket , new release bearing and plates and done a quiet clutch mod